In a hollow head, a technique for providing a rib on an inner surface of a crown has been disclosed. Japanese Patent No. 4262369 discloses a wood club head in which at least three ribs (A) and at least three ribs (B) are provided on the reverse surface of the crown. Slope angles of the ribs (A) and the ribs (B) are equal to or less than 45° relative to a face center line. The ribs (A) and the ribs (B) are sloped in opposite directions each other.
Japanese Patent Application Laid-Open No. 2012-45235 discloses a crown part on which a plurality of thick parts extending from a face side toward a back side are formed.